When a women becomes pregnant her body starts to produce a hormone called hCG (Human Chorionic Gonadotropin) This hormone give the positive result on both urine and blood based tests. hCG is produced by the embryo at implantation (when it starts to implant itself into the utering lining.) Implantation occurs 6-10 days after conception. As the embryo grows, the amount of hCG increases and doubles approximately every 2-3 days. The purpose of this hormone is to keep estrogen and progestone levels in proper balance until the placenta is adequately developed. Levels peak at 10 - 12 weeks at a level as high as 300,000 mIU/ml and then drop off.

Average Range of hCG Levels

Pregnant women will vary in levels of hCG within their body at different times. But once hCG levels beginning to build, they should not fall until after 10 - 12 weeks (LMP). A dramatic decline in hCG levels may indicate a miscarriage" and one should consult with their caregiver. The chart below gives an average range of mIU/ml of hCG in pregnant women from 3 - 26 weeks from last menstrual period. Please note that in multiple births hCG levels may raise faster. An hCG level of less than 5 mIU/ml generally indicates you are not pregnant.

Weeks from Last Menstrual Period (LMP)

Amount of hCG in mIU/ml

3

5 - 50

4

4 - 426

5

19 - 7,340

6

1,080 - 56,500

7 - 8

7,650 - 229,000

9 - 12

25,700 - 288,000

13 - 16

13,300 - 254,000

17 - 24

4,060 - 165,400

25 - 40

3,640 - 117,000

Pregnant women usually attain serum concentrations of 10 to 50 mIU in the week following conception. A maximum is reached by the second to third month, followed by a decrease in the third trimester.

Pregnancy Tests

Not all pregnancy tests are created equal. The more sensitive the test (the smaller amount of hCG it can detect), the earlier the opportunity to detect pregnancy. That means with a test sensitive to 20 mIU/ml hCG, a home pregnancy test is accurate as early as six to eight days after conception, well before your first missed period. NOTE: Conception may take place several days after date of intercourse, so the date of intercourse should not necessarily be viewed as the day of conception.

Brand

Detects

AimStick Dipstick

20 mIU

AimStep Cassette

20 mIU

Early-Pregnancy-Tests

20 mIU

AimStick Midstream (AccuHome)

25 mIU

Clearblue Easy (UK)

25 mIU

Day Seven (CDN)

25 mIU

Health Check

25 mIU

One Step Be Sure

25 mIU

Rapid Self-Test

25 mIU

E.P.T

40 mIU

Clearblue Easy (US)

50 mIU

Boots

50 mIU

Early Bird One Step

50 mIU

Early Pregnancy test

50 mIU

Hannaford

50 mIU

Rite-Aid

50 mIU

Selfcare

50 mIU

CVS

60 mIU

First Response

100 mIU

Answer

100 mIU

Conceive

100 mIU

Precise

100 mIU

Fact Plus

150-250mIU

Q: How soon after ovulation can I test?

A: The earliest you can get a positive result on the most sensitive pregnancy tests is seven days after ovulation. Implantation needs to occur before hCG is produced, and that generally happens between 6-12 days post ovulation, usually by 10 days after. For this reason, it makes economical sense to wait until 10-12 days after ovulation, but even then a significant percentage of women who are pregnant will still show a negative result. Many people won't have a positive HPT until the first day of a missed period or even a few days later.

Q: How accurate are home pregnancy tests on the first day of a missed period?

A: The highest possible screening sensitivity for an hCG-based pregnancy test (20-25 mIU/ml) conducted on the first day of a missed period is 90 percent, as 10 percent of women may not have implanted yet. With the same test, one week after the first day of the missed period the accuracy increases to 97 percent.

Q: What time of the day can I use the test?

Because home pregnancy tests detect hCG, diluted urine samples (from drinking large quantities of water) aren't recommended. It is best to collect urine samples containing the highest presence of the hCG hormone. First morning urine is the ideal sample as it contains the most concentrated presence of hCG. Otherwise, waiting several hours (4-5 minimum) is considered sufficient duration for an HPT.

Q: How do I use the test?

A: There are two types of HPT's -- test strips and midstream tests. For test strips, immerse the strip into the urine sample with the arrow end pointing towards the urine. Do not immerse past the MAX (Marker Line). Take the strip out after 3 seconds and lay the strip flat on a clean, dry, non-absorbent surface. Wait for colored bands to appear. Depending on the concentration of hCG in the test specimen, positive results may be observed in as little as 40 seconds. However, to confirm negative results, the complete reaction time of 5 minutes is required. Do not read results after the 5 minute reaction time.

With the pregnancy midstream test, hold by the handle so the absorbent tip, located on the bottom, is facing down. With the handle side of the test stick facing you and the twin absorbent tip pointing in a downward direction, hold the test stick in your stream of urine (and hold it for at least six seconds so that adequate urine contacts the absorbent end). Seal the absorbent windows with the cap. In 2 to 5 minutes, a rose-pink color band (control band) will appear in the window to show that the test is complete.

Q: How long do I wait to read the test?

A: A positive result can be seen as quickly as 40 seconds. You should not rely on any positive result that does not show up within the time limit (usually 5 minutes) stated in the test instructions. All pregnancy test brands have the possibility of displaying an evaporation line.

Q: How does a positive result look?

A: You should check the instructions that came with the HPT as there are some differences between the tests. Most of the tests have two windows -- one that tells you the test has been performed correctly (control), and one that gives you the positive or negative result. In the result window, the tests usually give a line or a plus. Any line, no matter how faint is considered a positive result. The color intensity of the test bands may vary since different stages of pregnancy have different concentrations of hCG hormone.

Examples of Line Tests

negative result

positive results

Examples of Plus/Minus Tests

negative result

positive results

Examples of Digital Tests

negative result

positive result

Q: Is a faint line still a positive?

If the test was read within the time limit, a positive line, no matter how varied the line colors, should be considered a positive result. All HPTs should be read within the time mentioned in the instructions and then thrown out to avoid confusion over evaporation lines.

Q: What if the test is negative after the 5 minute reaction time, but becomes positive after an hour?

A: You may be pregnant and just didn't have a high enough level of hCG to trigger the test within the usual time frame. Or that test may react over time, so you really need to test again either way in order to be sure of the result. Some brands indicate that an "evaporation line" will appear if the test is left to sit. Generally speaking, you should not rely on any positive result that does not show up within the time limit stated in the test instructions. All brands have the possibility of an evaporation line or chemical line.

If you think the result is incorrect, or if it is difficult to detect a line, repeat the test after 2 -3 days with a new test.

Using the test within 8 weeks of giving birth or having a miscarriage may also cause a false positive result. The test may detect hCG still in your system from a previous pregnancy You should ask your doctor for help in interpreting the result of your test if you have recently been pregnant.

Factors which should NOT affect the test result include alcohol, analgesics (pain killers), antibiotics, birth control pills or hormone therapies containing clomiphene citrate (Clomid or Serophen).

Q: Can I be pregnant and not get a positive HPT?

A: Yes. Most women will register on HPTs by the time they are a few days late for a period, but not everyone will. Factors that may result in a false negative are:

Inaccuracies in timing of the test or carelessness in the test procedure itself. Read the instructions carefully.